The present invention relates to a liquid crystal display (LCD) and a manufacturing method thereof.
Among the various flat panel displays, LCDs are popularly used for the display of information processing devices, such as mobile phone, personal computer, television, and personal digital assistant (PDA), due to thin thickness, light weight, low power consumption, and low electromagnetic radiation.
As shown in FIG. 1, a traditional LCD is formed by assembling an array glass substrate (TFT substrate) 110 and a color filter substrate (C/F substrate) 120, which are opposing with each other, with a sealant 130. A dielectric anisotropic liquid crystal layer 140 is disposed between the two substrates, one alignment layers 150 is provided on the inner side of each of the substrates, respectively, and a plurality of spacers 160 are formed on the surface of the substrates. When an electric field is applied between a pixel electrode on the TFT substrate and a counter electrode on the C/F substrate through a driving circuit 170, the orientation of the liquid crystal molecules are modified and the transmittance of the LCD can be changed to display images by controlling the magnitude of the applied electric field, along with a upper and a lower polarized plates 180 that are provided on the outer sides of the substrates, respectively. As image to be displayed becomes enrich, the requirement for display performance and image quality is improved, such as high luminance, high contrast, wide viewing angle, high response time, electrostatic protection, and minimal after-image.
After-image is one of the prominent defects in current LCDs. In general, after-image can be classified into plane after-image and line after-image. The plane after-image is generated from the direct current component in the driving voltage, which can be improved through the driving signal. Line after-image is common. After-image refers to a phenomenon that a previous image is retained on the screen of a LCD when the screen is switched from the previous image to a next image such as a low gray scale image after the previous image has been displayed on the screen for a long time. For example, a previous image of checkerboard is displayed for a long time as shown in FIG. 2A, a faint image of chessboard is left on the screen as in FIG. 2B when the screen is switched to a low gray scale image. The ions in the cell of the LCD move towards the upper and lower substrates along the direction of the applied electric field, respectively, and accumulate on the alignment layers during displaying. The accumulated ions generate static electricity. When the static electricity generated by the ions is high enough to change the transmittance of the liquid crystal layer, the display of the LCD will be affected disadvantageously. When the screen is switched to the next image, the accumulated ions cannot immediately leave the alignment layers and the previous image will remains, and thus after-image appears.
In theory, there are two methods to decrease the after-image. One is to reduce the amount of ions in the LCD. The ions in the panel mainly come from the material used, including the liquid crystal material, alignment layers, sealant, spacers, electrodes, and so on. A portion of the ions are brought in by the impure material, a portion of the ions are derived from the partial decomposition of the materials due to the applied voltage, high temperature, light illumination, and so on in a manufacturing process, and thus introduction of ions can be reduced by improving the purity of the materials. The other method is to improve the antistatic ability of the substrates of the LCD. The current method to improve the antistatic ability of the substrates mainly comprises improving the circuit design of the active elements of the TFT substrate, coating antistatic film on the surface of the substrates, and so on. However, the above methods cannot essentially eliminate the after-image.